The present invention relates, in general, to internal combustion engines and, more particularly, to cylinders in internal combustion engines.
Internal combustion engines have a cylinder block in which a plurality of hollow cylinder bores are formed. Pistons are reciprocally mounted within each cylinder and connected by piston rod at one end to a crank shaft so as to be driven between the typical four strokes of an internal combustion cycle. One and typically two metal piston rings are mounted on the piston to scrape carbon off the piston and cylinder wall as the piston moves upward in the cylinder to a top dead center position.
It is common for incomplete combustion of the air fuel mixture in the combustion chambers to cause carbon particles to be formed. These particles collect in the cylinder and are scraped off of the cylinder wall by the uppermost piston ring. Due to the high combustion temperatures to which the upper portion of the cylinder and the piston are exposed, the carbon particles fuse or sinter into a s solid mass forming a ridge or bulge on the upper portion of the cylinder wall typically at or just above the upper most movement position of the upper piston ring. Since the piston ring reciprocates thousands of times per minute during normal engine operation, the uppermost surface and, in particular, the sharp upper edge of the upper piston ring repeatedly and at high force levels slams into the ridge of fused carbon particles on the cylinder wall. This causes the desired sharp upper edge of the upper piston ring to grind away and gradually ground out to a small radius. This radius gradually increases over the life of the engine until the entire outer surface of the piston ring wears away. This increased wear causes the gap between the ends of the piston ring to expand which leads to increased combustion blowby past the upper piston ring.
As a consequence, a second carbon scraping piston ring is typically employed in most engine pistons to minimize the introduction of carbon particles into the engine oil.
It would be desirable to provide an engine cylinder construction which minimizes the build up of carbon particles on the cylinder wall. It would also be desirable to provide an internal combustion engine cylinder construction which minimizes the effect of carbon particle wear on the upper piston ring.